sensor setting
Primary current
. Taken from the sensor’s technical data, this
example sensor can be used with up to 4000 A application nominal current.
As the Rogowski sensor is linear and does not saturate, the 80 A/0.150 V at
50 Hz sensor also works as a 150 A/0.28125 V at 50 Hz sensor. When defining
another primary value for the sensor, also the nominal voltage has to be
redefined to maintain the same transformation ratio. However, the setting
in the protection relay (
Rated Secondary Value
) is not in V but in mV/Hz,
which makes the same setting
Rated Secondary Value
valid for both 50 and
60 Hz nominal frequency.
(Equation 1)
RSV
Rated Secondary Value
in mV/Hz
I
n
Application nominal current
I
pr
Sensor-rated primary current
f
n
Network nominal frequency
K
r
Sensor-rated voltage at the rated current in mV
In this example, the value is as calculated using the equation.
150
80
150
50
5 625
A
A
mV
Hz
mV
Hz
×
= .
(Equation 2)
With this information, the protection relay's current (Rogowski) sensor
settings can be set.
Table 92: Example setting values for current (Rogowski) sensor
Setting Value
Primary current 150 A
Rated secondary value 5.625 mV/Hz
When considering setting values for current sensor interfaces and for
protection functions utilizing these measurements, it should be noted
that the sensor measurement inputs in the relay have limits for linear
behavior. When this limit is exceeded, the input starts to saturate. The
saturation is reflected to the protection functions connected to the
sensor inputs. To ensure that the related protection functions operate
correctly, the start value setting for protection functions utilizing either
instantaneous or definite minimum time characteristics must not exceed
the linear measurement range. Furthermore, the effect on protection
functions utilizing inverse time characteristics should be considered. The
upper limit of the linear measurement range depends on the selected
application nominal current and the type of the current sensor used.
Table
93
shows the limits for an 80A/150mV 50Hz sensor.
Basic functions
1MRS759142 F
158 REX640
Technical Manual
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